1. Field of the Invention
The present invention relates to a plate used in light-shielding blades for which a high-speed motion is required, such as shutter blades for a focal-plane shutter, lens shutter or diaphragm blades.
2. Related Background Art
In recent years, with the improvement of film sensitivity and greater demand on image representations, higher shutter speeds have been required for cameras.
In order to increase the shutter speed, it may be possible to increase the driving force of the driving system. Then, a problem is encountered in that the capacity of a battery currently in use is not sufficient or in that its replacement is required sooner.
Therefore, it is necessary to lighten the blades per se. To lighten the blades, it would readily occur to make the blades thinner. However, making the blades thinner means substantially reducing rigidity, and there arises a so-called waving phenomenon, i.e., the blades are caused to wave in motion or at rest. The wave progress in the longitudinal direction.
If a shutter is driven when this waving phenomenon has been generated or is being generated, one blade may collide against another blade, a second group of blades or the housing frame which determines an image angle, leading to breakage.
Therefore, the plate member for the light shielding blades should be light yet highly rigid.
As a light-shielding blade member, there have been developed plate members such as disclosed in Japanese Patent Laid-Open Application No. 59-61827, Japanese Utility Model Laid-Open Application No. 60-63825, Japanese Patent Laid-Open Application No. 62-199439, and Japanese Patent Laid-Open Application No. 63-17435, which is structured with stacked layers formed with reinforced resin surface layers, each consisting of continuous carbon fibers oriented in one direction and matrix resin including this fiber, and a reinforced resin intermediate layer sandwiched by the two surface layers and consisting of continuous carbon fibers also oriented in one direction and a matrix resin including this fiber.
In these plate members, the longitudinal direction (orientation) of the carbon fiber of the surface layers and the longitudinal direction of the carbon fiber of the intermediate layer are orthogonal or almost orthogonal to each other in order to obtain isotropy.
The thickness of the plate member is approximately 60-120 .mu.m.
The plate members are stacked in symmetry with respect to a center plane in the thickness direction as a matter of course. Also, both the surface layers and intermediate layer are not necessarily limited to a single layer, but may be a layer produced by stacking a plurality of thin reinforced sheets.
By punching or cutting this plate member into a predetermined shape of the light shielding blades, it is possible to obtain approximately 20-50 light and highly strong and rigid light-shielding blades per plate member.
This type of light-shielding blade is practically used for a camera having a shutter speed of 1/8,000 second.